Synthetic fiber



Patented Sept. 20, 1938 ETD STAT SYNTHETIC FIBER Wallace Hume Carothers,Wilmington, Del., assignor to E. I. du Pont de Nemours & Company,Wilmington, Del., a corporation of Delaware No Drawing.

Application April 9, 1937,

Serial No. 136,031

56 Claims.

This invention relates to new compositions of matter, and moreparticularly to synthetic linear condensation polyamides and tofilaments, fibers, yarns, fabrics, and the like prepared therefrom.

The present application is a continuation-in-part of my applicationSerial Number 91,617, filed July 20, 1936, which is acontinuation-in-part of application Serial Number 74,811, filed April16, 1936, which is a continuation-in-part of abancloned applicationSerial Number 34,477, filed August 2, 1935, which in turn is acontinuationin-part of application Serial Number 181, filed January 2,1935; and of U. S. Patent 2,071,251, filed March 14, 1933; and of U. S.Patent 2,071,250, filed July 3, 1931.

Products obtained by the mutual reaction of certain dibasic carboxylicacids and certain organic diamines have in the past been described byvarious investigators. For the most part, these products have beencyclic amides of low molecular weight. In a few cases they have beensupposed to be polymeric, but they have been either of low molecularweight or completely infusible and insoluble. In all cases, they havebeen devoid of any known utility. These statements may be illustrated bythe following citations: Ann. 232, 227 (1886); Ber. 46, 2504 (1913);Ber. 5, 247 (1872); Ber. 17, 137 (1884); Ber. 27 R, 403 (1894); Ann.347, 17 (1906); Ann. 392, 92 (1912); J. A. C. S. 47, 2614 (1925).Insofar as I am aware, the prior art on synthetic polyamide fibers, andon polyamides capable of being drawn into useful fibers, isnon-existent.

This invention has as an object the preparation of new and valuablecompositions of matter, particularly synthetic fiber-forming materials.Another object is the preparation of filaments, fibers, and ribbons fromthese materials. A further object is the manufacture of yarns, fabrics,and the like from said filaments. Other objects will become apparent asthe description proceeds.

The first of these objects is accomplished by reacting together aprimary or secondary diamine (described comprehensively as a diaminehaving at least one hydrogen attached to each nitrogen) and either adicarboxylic acid or an amide-forming derivative of a dibasic carboXylicacid until a product is formed which can be drawn into a continuousoriented filament. The second object is attained by spinning thepolyamides into filaments, and preferably, subjecting the filaments tostress (cold drawing) thereby converting them into oriented filaments orfibers.

The third of these objects is accomplished by combining the filamentsinto a yarn and knitting, Weaving, or otherwise forming the yarn into afabric.

The term synthetic is used herein to imply 5 that the polyamides fromwhich my filaments are prepared are built up by a wholly artificialprocess and not by any natural process. In other words, my originalreactants are monomeric or relatively low molecular weight substances.

The term linear as used herein implies only those polyamides obtainablefrom bifunctional reactants. The structural units of such products arelinked end-to-end and in chain-like fashion. The term is intended toexclude three-dimensional polymeric structures, such as those that mightbe present in polymers derived from triamines or from tribasic acids.

The term polyamide is used to indicate a polymer containing a pluralityof amide linkages. In the linear condensation polyamides of thisinvention the amide-linkages appear in the chain of atoms which make upthe polymer.

The terms fiber-forming polyamide is used to indicate that my productsare capable of being 1 formed directly, i. e., without furtherpolymerization treatment, into useful fibers. As will be more fullyshown hereinafter, fiber-forming polyamides are highly polymerizedproducts and for the most part exhibit crystallinity in the massivestate.

The term filament as used herein refers to both the oriented andunoriented filaments or threads which are prepared from the polyamidesregardless of whether the filaments or threads 35 are long (continuous)or short (staple), large or small, while the term fiber will refer morespecifically to the oriented filaments or threads whether long or short,large or small.

The expression dibasic carboxylic acid is used to include carbonic acidand dicarboxylic acids. By amide-forming derivatives of dibasiccarboxylic acids I mean those materials such as anhydrides, amides, acidhalides, half esters, and diesters, which are known to form amides whenreacted with a primary or secondary amine.

The following discussion will make clear the nature of the products fromwhich my filaments and fibers are prepared, and the meaning of 50 theabove and other terms used hereinafter. If a dicarboxylic acid and adiamine are heated together under such conditions as to permit amideformation, it can readily be seen that the reaction might proceed insuch a way as to yield a linear polyamide The indicated formula, inwhich G and G represent divalent hydrocarbon radicals, represents theproduct as being composed of long chains built up from a series ofidentical units This unit, derived from one molecule each of acid anddiamine, may be called the structural unit. It will be convenient torefer to the number of atoms in the chain of this unit as the unitlength. The expression radical of a dibasic carboxylic acid is taken tomean that fragment or divalent radical remaining after the two acidichydroxyls have been removed from its formula. Thus the radical ofcarbonic acid is -CO; the radical of adipic acid is The expressionradical of a diamine indicates the divalent radical or fragmentremaining after one hydrogen has been removed from each amino group.Thus the radical of pentamethylenediamine is NHCH2CH2-CH2-CH2CH2NH.

The radical length is, in the case of both acid and amine, the number ofatoms in the chain of the radical. Thus the radical length of carbonicacid is 1; that of adipic acid is 6; and that of pentamethylenediamineis 7. The term unit length, referred to above, obviously means the sumof the radical lengths of the diamine and the acid. Thus, the unitlength of polypentamethylene sebacamide, the polyamide derived fromsebacic acid and pentamethylenediamine, is 17.

As previously mentioned, fiber-forming polyamides can be prepared byreacting diamines with dicarboxylic acids or amide-forming derivativesof dibasic carboxylic acids, of which the most suitable are the diesterswith volatile monohydric alcohols or phenols. The diamines suitable forthe practice of my invention are those having at least one hydrogenattached to each of the nitrogen atoms. In other words, I may usedi-primary amines, primary-secondary amines, or di-secondary amines, butnever a diamine in which either amino group is tertiary. Of all thesetypes, of amines, the di-primary amines are in the great majority ofinstances far more satisfactory because of their greater reactivity andbecause they yield polyamides of higher melting points. Within the fieldof diprimary amines, the aliphatic amines are most suitable for theready preparation of polyamides capable of being drawn into the highestquality fibers. By aliphatic diamine as used herein is meant a diaminein which the nitrogens. are attached to aliphatic carbons, (i. e.,carbon atoms which are not a part of an aromatic ring). Mixtures ofdiamines of any of the mentioned operable types may also be used.Fiber-forming polyamides may also be prepared from one or more diaminesand (a) mixtures of different dicarboxylic acids (b) mixtures ofamide-forming derivatives of different dibasic carboxylic acids (0)mixtures of dicarboxylic acids and/or amideforming derivatives ofdibasic carboxylic acids with one or more monoaminomonocarboxylic acidsor amide-forming derivatives thereof.

While the fiber-forming polyamides used in my invention can be preparedfrom a wide variety of diamines and dicarboxylic acids 'or amideforiningderivatives of dibasic carboxylic acids, I have found that a preferredselection of amine and acid is that in which the sum of the radicallengths is at least 9. Such a pair of reactants has very little if anytendency to form low molecular weight cyclic amides, and the polyamidestherefrom are more generally soluble or fusible, one of these propertiesbeing necessary for spinning. I have, however, met with some success inpreparing fiber-forming polyamides from amines and acids the sum ofwhose radical lengths is less than 9. As an example of a fiber-formingpolyamide having a relatively short structural unit may be mentionedthat from pentamethylenediamine and dibutyl carbonate.

Of the fiber-forming polyamides having a unit length-of at least 9, avery useful group from the standpoint of fiber qualities are thosederived from diamines of formula NH2CH2RCH2NH2 and dicarboxylic acids offormula or amide-forming derivatives thereof, in which R and R aredivalent hydrocarbon radicals free from olefinic and acetylenicunsaturation (i. e., non-benzenoid unsaturation) and in which R has achain length of at least two carbon atoms. The R and R. may bealiphatic, alicyclic, aromatic, or araliphatic radicals. Of this groupof polyamides, those in which R. is (0mm and R. is (Cfmy where :c and yare integers and a: is at least two, are especially useful from thestandpoint of spinnability and fiber qualities. They are easily obtainedat an appropriate viscosity for spinning and have a type ofcrystallinity which enables them to be cold drawn with especialfacility. As valuable members of this class may be mentionedpolypentamethylene adipamide, polyhexamethylene adipamide,polyoctamethylene .adipamide, polydecamethylene adipamide,polypentamethylene suberamide, polyhexamethylene suberamide,polydecamethylene suberamide, polypentamethylene sebacamide,polyhexamethylene sebacamide, and polyoctamethylene sebacamide.

My fiber-forming polyamides are prepared by heating in substantiallyequimolecular amounts a diamine and a dicarboxylic acid or anamideforming derivative of a dibasic carboxylic acid under condensationpolymerization conditions, generally 180 to 300 C., in the presence orabsence of a diluent, until the product has a sufficiently highmolecular Weight to exhibit fiberforming properties. The fiber-formingstage can be tested for by touching the molten polymer with a rod anddrawing the rod away; if this stage has been reached, a continuousfilament of considerable strength and pliability is readily formed. Thisstage is reached essentially when the polyamide has an intrinsicviscosity of about 0.4, where intrinsic viscosity is defined as ge M cin which M is the viscosity of a dilute solution (e. g., 0.5%concentration) of the polymer in m-cresol divided by the viscosity ofm-cresol in the same units and at the same temperature (8. g., 25centigrade) and C is the concentration in grams of polymer per cc. ofsolution. If products capable of being formed into fibers of optimumquality are to be obtained, it is desira- 'ble to prolong the heatingbeyond that point Where the intrinsic viscosity has become 0.4. Ingeneral products having an intrinsic viscosity between 0.5 and 2.0 aremost useful for the preparation of fibers.

In common with other condensation polymerization products thefiber-forming polyamides will in general comprise a series ofindividuals of closely similar structure. The average size of theseindividuals, i. e., the average molecular weight of the polymer, issubject to deliberate control within certain limits; the further thereaction has progressed the higher the average molecular weight (andintrinsic viscosity) will be. If the reactants are used in exactlyequimolecular amounts and the heating is continued for a long time underconditions which permit the escape of the volatile products, polyamidesof very high molecular weight are obtained. However, if either reactantis used in excess, the polymerization proceeds to a certain point andthen essentially stops. The point at which polymerization ceases isdependent upon the amount of diamine or dibasic acid (or derivative)used in excess. The reactant added in excess is spoken of as a viscositystabilizer and the polymer obtained with its use is spoken of as aviscosity stable polymer, since its intrinsic viscosity is not alteredappreciably by further heating at spinning temperatures. Polyamides ofalmost any intrinsic viscosity can be prepared by selecting the properamount of stabilizer. In general from 0.1 to 5.0% excess reactant isused in making viscosity stable polyamides. The viscosity stablepolyamides are particularly useful in spinning filaments from melt sincethey do not change appreciably in viscosity during the course of thespinning operation.

In general my fiber-forming polyamides are prepared most economicallyfrom a diamine and a dicarboxylic acid. The first reaction which occurswhen a diamine and a dicarboxylic acid are mixed and brought intosumciently intimate contact is the formation of the diamine-dicarboxylicacid salt. Such salts are generally solids and since their tendency todissociate into their components is relatively low, both the acid andamine are fixed. The mixture can therefore be subjected immediately toheat in an open vessel without danger of losing amine or acid and sodisturbing the balance in the proportion of reactants. Frequently,however, it is advantageous to isolate the salt and purify it prior toconversion into the polyamide. The preparation of the salts affords anautomatic means for adjusting the amine and acid reactants tosubstantial equivalency and it avoids the diificulty attendant upon thepreservation of the isolated amines in the state of purity. It alsotends to eliminate impurities present in the original diamine anddicarboxylic acid.

A convenient method of preparing these salts consists in mixingapproximately chemical equivalent amounts of the diamine and thedicarboxylic acid in a liquid which is a poor solvent for the resultantsalt. The salt which separates from the liquid can then be purified, ifdesired, by crystallization from a suitable solvent. The salts arecrystalline and have definite melting points. They are, as a rule,soluble in water and may conveniently be crystallized from certainalcohols and alcohol-Water mixtures. They are relatively insoluble inacetone, benzene, and ether.

The preparation of fiber-forming polyamides from thediamine-dicarboxylic acid salts can be carried out in a number of ways.The salt may be heated in the absence of a solvent or diluent (fusionmethod) to reaction temperature (usually 180-300 C.) under conditionswhich permit the removal of the water formed in the reaction, untilexamination of the test portion indicates that the product has goodfiber-forming qualities. It is desirable to subject the polyamide toreduced pressure, e. g., an absolute pressure equivalent to 50 to 300mm. of mercury, before using it in making filaments and other shapedobjects. This is conveniently done by evacuating the reaction vessel inwhich the polyamide is prepared before allowing the polymer to solidify.Another procedure for preparing polyamides consists in heating a salt inan inert solvent for the polymer, preferably a monohydric phenol such asphenol, m-cresol, o-cresol, p-cresol, xylenol, p-butyl phenol, thymol,diphenylolpropane, and o-hydroxydiphenyl. With the solvents may beassociated, if desired, non-solvents which are nonreactive, such ashydrocarbons, chlorinated hydrocarbons, etc. When the reaction hasproceeded far enough to give a polymer of good fiber-forming qualities,the mixture can be removed from the reaction vessel and used as such (e.g., for spinning from solution) or the polymer can be separated from thesolvent by precipitation, i. e., by mixing with a non-solvent for thepolymer such as alcohol, ethyl acetate, or a mixture of the two. Stillanother method of preparation consists in heating the salt in thepresence of an inert non-solvent for the polymer such as high boilinghydrocarbons of which white medicinal oil may be mentioned. The methodscan also be applied directly to the diamine and dicarboxylic acidwithout first isolating the salt.

In place of using the diamine and dicarboxylic acid (or the salt), adiamine and an amidefcrming derivative of a dibasic carboxylic acid maybe used in the preparation of the polyamide. The reaction may be carriedout in the absence of a solvent, in the presence of a solvent, in thepresence of a diluent which is not a solvent for the polymer, or in thepresence of a, mixture of solvent and diluent. The reaction conditions,as indicated in my co-pending application Serial Number 181, differsomewhat with the nature of the amide-forming derivative used. Forexample, the esters of dibasic carboxylic acids, and particularly thearyl esters, react with diamines at a lower temperature than do theacids themselves, often at temperatures as low as 50 C. In a specificexperiment hexamethylenediamine and dicresyl adipate yielded afiber-forming polyamide in 2.5 hours heating at C.

The polyamides of this invention compared with most organic compoundsare fairly resistant to oxidation. Nevertheless, at the hightemperatures used in their preparation (e. g., 250 C.) they show astrong tendency to become discolored in the presence of air. For thisreason, it is desirable to exclude air or to limit the access of airduring their preparation. This may be done by operating in a closedvessel during the early stages of the reaction, or, if an open vessel isused, by providing a stream of inert gas. It is helpful in some cases toadd antioxidants to the reaction mixture, especially antioxidants suchas syringic acid that show very little inherent tendency to discolor. Itis also important to exclude oxygen from the polymer during spinning.

In general, no added catalysts are required in the above describedprocesses of the present invention. It should be mentioned, however,that the surface of the reaction vessel (e. g., glass) appears toexercise a certain degree of catalytic function in many cases. The useof added catalysts sometimes confers additional advantages. Examples ofsuch materials are inorganic materials of alkaline reaction such asoxides and carbonates, and acidic materials such as halogen salts ofpolyvalent metals, for example, stannous chloride.

The polyamides can be prepared in reactors constructed of or lined withglass, porcelain, enamel, silver, gold, tantalum, platinum, palladium,rhodium, alloys of platinum with palladium and/or rhodium, chromiumplated metals, and chromium containing ferrous metals, includingchromium-nickel steels. In order to obtain lightcolored products it isgenerally necessary to carry out the reaction in substantially completeabsence of oxygen. This means that if commercial nitrogen is maintainedover or passed through the reaction mixture it should be washed free ofoxygen. As examples of other inert gases which may be used to blanketthe polymer during preparation or spinning may be mentioned carbondioxide and hydrogen.

The properties of a given polyamide will vary over a considerable range,depending upon its molecular weight and in part on the nature of itsterminal groups which in turn is dependent upon which reactant was usedin excess. The average molecular weights of the polyamides are verydifficult to determine on account of their limited solubility insuitable solvents. A precise knowledge of average molecular weights is,however, not important for the purposes of this invention. In a roughway it may be said that two stages or degrees of polymerization exist:low polymers whose molecular weights probably lie in the neighborhood of1000 to 4000, and fiberforming polyamides whose molecular weightsprobably lie above 7000. The most obvious distinction between lowpolymers and the high polymers or superpolymers is that the former whenmolten are relatively less viscous. The high polymers even attemperatures 25 C. above their melting points are quite viscous. Thehigh polymers also dissolve more slowly than the low polymers andsolution is preceded by swelling. Practically the most importantdistinction between the two types is that the high polymers are readilyspun into strong, continuous, pliable, permanently oriented fibers,while this property is lacking in the low polymers. In general the lowpolymers, and in particular those having a unit length of at least 9,can be converted into high polymers by a continuation of the reaction bywhich the low polymers were formed.

Two of the most characteristic properties of the fiber-formingpolyamides used in this invention are their high melting points and lowsolubilities. Those derived from. the simpler types of amines and acidsare almost invariably opaque solids that melt or become transparent at afairly definite temperature. Below their melting points thefiber-forming polyamides when examined by X-rays generally furnish sharpX-ray crystalline powder diifraction patterns, which is evidence oftheir crystalline structure in the massive state. Densities of thesepolyamides generally lie between 1.0 and 1.2, which is considerablylower than that of previously described artificial fiber-formingmaterials. Their refractive index is usually in the neighborhood of1.53. Typical melting points are shown in Table I. All of the polyamidesin this table are capable of being spun into continuous filaments.

TABLE I Approximate melting points of some fiberjorming polyamidesPolyamide derived irom M. P. C.

Ethylenediaminc and sebacic acid 254 'letramethylenediamine and adipicacid" 278 Tetramethylonediamine and suberic acid... 250'letramethylenediamine and azelaic acid 223 Tetrametliylenediamine andscbacic acid- 239 'letramethylenediamlne and undecandioic ac 208Pentamethylenediamine and malonic acid"... 191 Pcntalnethylenediamineand glutaric acid 198 Pentamethylenediamlne and adipic aci(l, 223Pentamethylenediamine and pimclic acid. 183 Pentamcthylenediamine andsubcric acid-.. 202 Pentamethylencdiamine and azelaic acid 178Pentamethylencdiamine and undecandioic acid 173 Pcutamethylenediamineand brassylic acid 176 Pentamethylcnediamine and tetradecancdioic acid.Pcntamethylenediamine and octadecauedioic acid. 167 Hexamethylcnediamincand sebacic acid .l 209 llexarnethylenadiamine and beta-methyl adipicacid. 216 Hexagncthyleucdiamine and l, 2cyclol1exanediacetic 255 amOctamctliylcnediarninc and adipic acid 235 Octamethylenediamine andsebacic acid l9! Dec-amethylenediamine and carbonic acid 200Decamethyleuedlamine and oxalic acid. 229 Decamcthylenediamine andsebacic acid 10 1 Dccamcthylenediamiue and para-phenylene acid 2'12Para-xylylcnediamine and sebacic acid 20S 3-Hcthylhexamethylcnediamincand adipic acid 180 Pipcrazine and sebacic acid 153llexamethylencdiamine and diphcnic acid 157 The melting points aredependent to some extent upon the heating schedule used and theconditions of thermal contact, but when. carried out by the sameoperator under the same conditions they are fairly sharp andreproducible. The melting points indicated in the table were determinedby placing fine particles of the polyamide on a heated metal block inthe presence of air and noting the temperature of melting or fusion.Values obtained in this way are usually from 5 to 20 C. lower than thoseobtained by noting the temperature at which the polyamide melts whenheated in a glass tube in the absence of oxygen. The melting points areconsiderably affected by the nature of the acid and the diamine used intheir preparation. In particular melting points generally diminish withincreasing unit length and increasing degree of substitution on thehydrocarbon chain. Increased solubility also runs in. the samedirection, but is not greatly afiected by the molecular weight. For themost part, the polyamides used in the; preparation of the filaments andfibers of this invention can be dissolved in hot glacial acetic acid, informic acid, or in phenols, but are quite insoluble in most of the otherusual types of organic solvents. However, polyamides derived fromreactants having a hydrocarbon. side chain, e. g., 3methylhexamethylenediamine, betamethyl adipic acid, and the like, aresoluble in a wider range of solvents including alcohols. This is oftentrue also of interpolymers or copolymers, i. e., polyamides derived froma mixture of reactants capable of yielding more than one polyamide ifreacted in suitable combinations. Thus, the interpolyamide derived fromequimolecular amounts of hexamethylcne diammonium adipate anddecamethylene diammonium sebacate is soluble in ethanol and butanol.

In the finely divided state or in the form of filaments and fibers thepolyamides of this invention are attacked by strong mineral acids, suchas hydrochloric or sulfuric acid, and on heating with such acids theyare hydrolyzed to the dibasic acids and diamines from which they arederived. When reference is made in the claims to the formation of a.diamine by acid hydrolysis, it is to be understood that the termincludes the mineral acid salt of the diamine. The polyamides areresistant to attack by strong caustic alkalies but these agencies alsowill finally hydrolyze them to the diamines and dibasic acids.

The polyamides of this invention can be spun into continuous filamentsin a number of ways. They can be spun directly from the reaction vesselin which they are prepared by attaching a suitable spinneret to thebottom thereof or they can be removed and spun from a separate device.

vOne method of spinning (wet process) consists in dissolving thepolyamide in a suitable solvent and extruding the resulting solutionthrough orifices into a liquid which dissolves the solvent but not thepolyamide, and continuously collecting the filaments thus formed on asuitable revolving drum or spindle. Another method (dry process)consists in extruding a solution of the polyamide into a heated chamberwhere the solvent is removed by evaporation. Still another method (meltprocess) consists in extruding the molten polyamide through orificesinto the atmosphere where it congeals into a filament. In these variousmethods of spinning the fiberforming mass may be forced through theorifices by means of gas pressure or by means of a constant volumedelivery pump. By similar processes the'polyamides can be formed intorods, bristles, sheets, foils, ribbons, films, and the like. In thevarious methods of forming shaped articles from fiber-formingpolyamides, and particularly when this is done from solutions of thepolymers, the characteristics of the filaments, etc., may be altered byblending the polyamides with other polyamides or with resins,plasticizers, cellulose derivatives, etc. As cellulose derivatives whichcan be blended with the polyamide solutions might be mentioned ethylcellulose, benzyl cellulose, and cellulose acetate.

A remarkable characteristic of filaments of this invention is theirability to accept a very high degree of permanent orientation understress. Although the unoriented or slightly oriented filaments aresuificiently pliable and strong for some purposes the highly orientedfilaments or fibers are in general more useful. Filaments obtained byspinning the polyamides under such.

conditions that no stress is applied closely resemblethe polymer fromwhich they are spun. In particular, when examined by X-rays theygenerally furnish X-ray crystalline powder diffraction patterns.However, although ordinary spinning conditions, and especially withcertain polyamides, e. g., polypentamethylene sebacamide, may produce afilament that shows by the X-ray test orientation in some degree,nevertheless it is advantageous to subject the filaments subsequently toa cold drawing process (i. e., stretching below the melting point offilament). By this cold drawing the filaments can be elongated as muchas 200 to 700%. The elongation is accompanied by a progressive increasein tensile strength until a definite limit is reached beyond which theapplication of additional stress causes the fiber to break. Thecold-drawn filaments remain permanently extended, they are much strongerthan the material from which they are drawn, more elastic, and whenexamined by X- rays they furnish a sharp diffraction fiber pattern. Theyalso exhibit strong birefringence and.

parallel extinction when observed under crossed Nicol prisms. Thisevidence of fiber orientation shows that the cold drawn filaments aretrue fibers. The fibers can be doubled and/or'twisted into threads oryarns suitable for the manufacture of fabrics. Sometimes it is desirableto set the twist in these yarns by means of heat, preferably by steamtreatment. If desired, the filaments used in the preparation of thefibers can be twisted before cold drawing.

When the wet process is used in spinning synthetic linear condensationpolyamides, it is desirable to use polymers having an intrinsicviscosity of at least 1.0. Polymers of lower intrinsic viscosity can beused with some success, however, by using high concentrations of polymerand by extruding the solvent from the spinneret at elevatedtemperatures, e. g., 100-200 0. Especially useful solvents for the wetspinning process are phenol and formic acid. In the case of certainpolyamides, e. g., polyhexamethylene betamethyl adipamide, alcohols canbe used as solvents. Other solvents which may be used include variousphenols, e. g., cresol and xylenol; lower fatty acids, such as acetic,chloracetic, propionic, and butyric; and, if elevated temperatures areavoided, certain chlorohydrins, such as epichlorohydrin and glyceroldichlorohydrin, and certain mineral acids, e. g., hydrochloric,sulfuric, and hydrofluoric, Anhydrous hydrogen fluoride is a goodpolyamide solvent. Mixtures of these solvents can also be used.Moreover, the solvents may be diluted with non-solvents, such as water,dioxane, isobutanol, chloroform, benzene, and the like. The presenceofthe non-solvent increases the rate of coagulation in the spinning bath.The concentration of the polyamide solutions required for successfulspinning vary with the intrinsic viscosity of the polyamide used.Polymers of high intrinsic viscosity can be spun at lower concentrationsthan those of lower intrinsic viscosity. When phenol alone is used assolvent, it is necessary to operate at elevated temperature, generallyabove 75 C. and preferably in the range of IOU-200 C. depending upon theconcentration and intrinsic viscosity of the polyamide. These phenolsolutions gel at room temperature. At the elevated temperature requiredto spin such solutions, it is generally impossible to immerse thespinneret in the coagulating bath as is done in normal wet spinningpractice unless the temperature of the coagulating bath is keptsufficiently high. If, however, the phenol solution is diluted with asuitable amount of non-solvent, preferably water, it is possible to spinat ordinary temperatures and to immerse the spinneret in the coagulatingbath. Solutions of polymer in 85-95% phenol (5-15% water) can be spun inthis way at ordinary temperatures. This method of spinning is moresatisfactory than spinning from anhydrous phenol.

The spinning or coagulating bath used in Wet spinning consists of aliquid which dissolves the polyamide solvent but not the polyamideitself. The spinning bath should gel the polymer rather than precipitateit. The coagulating process differs from that which occurs in viscosespinning in that the fiber-forming material does not undergo a chemicalchange during the process. The coagulating liquid selected will dependin part on the nature of the solvent from which the polyamide is spun.In spinning polyamides from a phenol or acid solution, aqueous alkalinespinning baths, particularly dilute solutions of sodium hydroxide orsodium sulfide (preferably 2-10%) concentration are very useful. Varioussalts, e. g., sodium tartrate, disodium phosphate and sodium citrate,can be added to these alkaline baths. The addition of wetting agents issometimes helpful. Many organic liquids which are non-solvents for thepolyamides, such as esters, ethers, ketones, and amines can also beused. As examples of such substances might be mentioned ethyl butyrate,glycol acetate, diethyl succinate, dioxane, dibutyl ether, methyl hexylketone, pyridine, toluene, xylene, and kerosene. In general, the aqueousalkaline baths cause more rapid coagulation of the polyamides than dobaths composed of organic solvents. Increasing the temperature of thebath also increases the rate of coagulation; temperatures of 40-80" C.are very suitable.

Inorder to obtain filaments of satisfactory strength in the wet spinningprocess, drawing of the filaments in the bath should be avoided as muchas possible until coagulation is complete. Stretching in the bath can beminimized by running the filaments over a motor driven guide rollimmediately after entering the bath. The size (i. e., the length) of thespinning bath required will depend somewhat upon the nature of thepolyamide solution and of the coagulating liquid but also upon the rateof spinning. In general, a bath seven feet in length is sufilcient. Thefilaments can be cold drawn after coagulation is substantially complete.Cold drawing may be carried out in the coagulating bath, but ispreferably done outside of the bath either before or after washing thefilaments. It is preferable to carry out the cold drawing operationwhile the filaments are still wet. Very fine filaments can be spun bythe wet process; in fact, spinning improves as the denier of the fiberis decreased. The process is best adapted to the preparation offilaments having a denier below 1.5. In contrast to the melt spinningprocess, the fibers obtained by this method usually have an irregularcrenulated surface; in other words, a cross-section of the fiberpresents an irregular area. For certain uses, e. g., in the preparationof staple, this is an advantage. The crenulated surface aids in theformation of threads and yarns from the staple. Polyamide staple can bespun into yarns and fabrics in much the same fashion as cotton.

The dry spinning process, like the wet spinning process, is best carriedout with polyamides having an intrinsic viscosity of at least 1.0.However, polymers of lower intrinsic viscosity can be spun with somesuccess by employing high concentrations and elevated temperatures. Thesolvents used in the dry spinning process should preferably be ofrelatively low boiling point so that they can be volatilized without toomuch difficulty. Formic acid is an exceptionally useful solvent for thispurpose. However, phenol and the other solvents mentioned in connectionwith the wet spinning process can also be used. Nonsolvents may be addedto the polymer solution but are in general undesirable. Plasticizers maybe added to the solutions if desired, but the nature of the fibers issuch that no flexibilizing agents are necessary. Dry spinning issuitably carried out in a heated vertical chamber or cell which isprovided with a spinneret at the top and an opening at the bottom forremoving the filaments. The spinneret may be of the conventional rayontype (fiat face); the filaments are readily thrown free of the spinneretwith substantially no fouling of the spinneret face. A current of air orother gas is maintained in the drying chamber to aid in the removal ofthe solvent. The dry spinning of formic acid solutions of polyamides canbe performed satisfactorily with head temperatures (temperature ofsolution in the spinneret) of 20 to 110 C. and cell temperatures(temperature of drying or evaporating chamber) of to 120 C. If thedrying chamber is maintained under reduced pressLu-e, lower celltemperatures can be used. The concentration of the solution mostsatisfactory for dry spinning will depend upon the intrinsic viscosityof the polymer and the spinning temperatures to be employed. Generally,it is desirable to use solutions having an absolute viscosity of atleast 200 poises at the spinning temperature. The polyamide solutionpasses through the orifices into the spinning chamber, evaporation ofsol vents starts immediately and the extruded portion sets up to afilament. After the major portion of the solvent has been removed, andpreferably after substantially complete removal of the solvent has takenplace, the filaments can be cold-drawn into oriented fibers. The colddrawing can be carried out Within the heating chamber, but preferably itis done outside the heating chamber, either as an integral part of thespinning operation or as a separate step. Fibers obtained by the dryprocess, like those obtained in the Wet method, generally have surfaceswhich are crenulated.

The polyamides of this invention are of such extraordinary nature thatthey are also capable of being spun into continuous filaments directlyfrom the molten mass without addition of any solvent or plasticizer. Forthis purpose a mass of the molten polymer may be touched with a rod.Upon drawing the rod away a filament is formed. The filament may becaught on a moving drum or reel and in this manner a continuous filamentmay be drawn from the molten mass until the latter is exhausted. Thecross-section of the filaments thus obtained can be regulated bycontrolling the temperature of the molten mass and the rate of reeling.The higher the temperature and the more rapid the rate of reeling, thefiner will be the filament.

Continuous filaments may also be produced by extruding the moltenpolyamide through an orifice, or through a spinneret containing aplurality of orifices, and continuously collecting the extrudedfilaments on a rotating drum. The fineness of the filaments may becontrolled by controlling the temperature of the molten polymer, theamount of pressure applied or the rate of pumping, the size of theorifices, and the rate of reeling. It is possible to spin polyamidefilaments at very high speeds, e. g., 3000 feet per minute. Theproperties of the polyamides of this invention also make it possible toobtain exceedingly fine filaments, as fine as 0.2 denier or less. Theoptimum temperature for the spinning of each polyamide must be workedout experimentally. Below this optimum temperature filaments of inferiorquality are obtained; above this temperature the polyamide mass is toofluid for ready spinning and may be subject to decomposition. Thus, forpolyhexamethylene adipamide the optimum melt spinning temperature liesbetween 285 and 295 C., although this depends somewhat on the spinningassembly. In spinning the polyamides from melt it is also important thatoxygen be excluded from the molten polymer.

In the melt spinning process the formation of continuous oriented fibersfrom the filaments of this invention may be easily conducted as anintegral part of the spinning operation. Thus, the extruded filaments asthey are collected may be transferred continuously to a second drumdriven at a higher rate of speed, so as to provide any desired degree ofstretching or cold drawing. Friction devices may also be used to providethe necessary stretch. Cold drawing can also be effected by drawing thefilaments through a die having an orifice smaller than that of theundrawn filament but larger than that of the cold drawn filament. It maybe observed that these processes of cold drawing differ from thestretch-spinning known to the artificial fiber art in that they may becarried out very rapidly and completely in the total absence of anysolvent or plasticizer. However, the stretching can also be efiected inthe presence of solvent orplasticizer. It is generally desirable tocarry out the spinning and handling of the polyamides in a moistatmosphere or to sprinkle the filaments with water since this destroysthe electrostatic charges on the filaments. Moreover, the wet filamentscold draw better than dry filaments. v

Still another method for obtaining filaments from synthetic linearcondensation polyamides and other polymers of this type consists infeeding the polymer in convenient form, e. g., a small rod, through aspray gun in which it is melted by an oxyacetylene flame, or othersuitable device, and atomized or reduced to very fine filamentsimmediately by a blast of nitrogen or other gas. The polymer leaves thegun in the form of fine filaments resembling a spider web. Thesefilaments can be used in making yarns, etc., which can be cold drawn. Byimpinging the blast from the spray gun directly on a proper backing, thepolymer can be obtained in the form of a continuous coating.

The properties of the fibers of this invention vary considerably withthe nature of the reactants used in preparing the polyamides, and withthe conditions of reaction and spinning. General characteristicsillustrated in Example I are high tenacity, high orientation, lack ofsensitivity toward conditions of humidity, exceptionally good elasticrecovery, extraordinary resistance to solvents and chemical agents, andexceptionally good ageing characteristics in air even at elevatedtemperatures, It is possible to tie hard knots in polyamide fiberswithout materially decreasing their tenacity. The tenacity of the fibersis greater than 1.1 g. per denier and usually above 3.0 g. per denier.Most of the fibers have tenaci ties ranging from 3 to 7 g. per denier.The fibers have a strong affinity for dyes; they can be dyed rapidly,permanently and directly, with the dyes ordinarily used for W001 andsilk. In general, fibers prepared from dibasic acid-stabilized polymerstake up basic dyes more readily than those made from diamine-stabilizedpolymers, while the latter have a stronger affinity for acid dyes.

The following examples, in which the parts are given by weight, areillustrative of this invention:

Example I A mixture of 14.8 parts of pentamethylenediamine, 29.3 partsof sebacic acid, and 44 parts of mixed xylenols (B. P. 218-222 C.) wasplaced in a vessel fitted with a conductivity cell, a means forreturning solvent lost by distillation, a means for introducingnitrogen, a thermometer, and a viscometer. The mixture was heated for 13hours by means of the vapors of boiling naphthalene (218 C.), duringwhich period the conductivity and viscosity were'measured at appropriateintervals. The conductivity dropped rapidly and the viscosity rosesteadily. At the end of 13 hours, the intrinsicviscosity was 0.62, andthe conductivity had dropped from an initial value of 0.0028 mhos to afinal one of 0.000053 mhos. At this point, examination of a smallportion of the product, separated by precipitation in alcohol andsubsequent fusion, showed that it could be drawn into fibers ofexcellent strength. The entire reaction mass was then poured graduallywith stirring into a large volume of ethyl alcohol. The polyamideprecipitated as a white granular powder, and was filtered, washed withalcohol, and dried. It melted at 195196 C. in air on a heated metalblock. Analysis of the above product shows that it has the formulaContinuous filaments were prepared from the product as follows: A samplewas heated at 234 C. in a cylindrical metal vessel surrounded by anelectrically heated metal block and provided at the bottom with anorifice 0.47 mm. in diameter. The top of the vessel was connected with atube through which nitrogen was passed under a gauge pressureto 3 lbs.The extruded filament was collected on amotor-driven drum having aperipheral speed of 82 feet per minute and was continuously transferredto and collected on a second drum having a peripheral speed of 164 feetper minute. The extent of the cold drawing thus produced was 100%. Theresulting fiber was lustrous and silky in appearance. It showed strongbirefringence with parallel extinction under crossed Nicol prisms andwhen examined by X-rays it furnished a sharp fiber diffraction pattern,while the same material before spinning furnished only a, crystallinepowder diffraction pattern. When further stress was applied to thesefibers cold drawing occurred up to a total final length of 452%.Physical data on the completely cold drawn fibers were: denier at break,0.63; tensile at break, 50.5 kg./sq. mm. or 5.2 g. per denier. Theelastic recovery of these fibers under moderate elongations or stresseswas very remarkable and in this respect it was much superior to existingartificial silks. In their physical behavior these fibers are almostcompletely insensitive to moisture. The fibers are completely resistantto the common organic solvents ex cept such materials as hot aceticacid, formic acid or phenol, and they can for example be immersed inboiling toluene for a week without any noticeable effect. They are alsovery resistant to the effects of air and high temperature. They show nosigns of tendering after storage for a month in air at 110 C. However,on heating with strong mineral acid, such as hydrochloric, hydrobromic,sulfuric, or phosphoric, these fibers disintegrate and are hydrolyzed tosebacic acid and pentamethylenediamine (mineral acid salt).

Polypentamethylene sebacamide (intrinsic viscosity 0.67) prepared byheating purified pentamethylenediamine-sebacic acid salt for 'threehours under conditions similar to those described above was spun intofibers (250% cold drawing, applied in two stages) having a denier of 4.9and a tenacity at break of 7.1 g. per denier. These fibers were pliedinto a 123-denier, Z l-filament yarn having four twists per inch. Thisyarn was then knit into a fabric and compared with a similar fabricknitted from 95-denier, 7- thread, 10-turn silk. The polyamide fabricwas found to have far better elastic recovery than natural silk,particularly under conditions of high stretch (100%), high humidity(85%) or wet, and for long periods of time (15 hours). This isillustrated by Table 11.

TABLE II Elastic recovery of knitted fabric Silk recovery 3 83 53}?Percent Time Relaxastretollcd held tion r 0 5 Wet 5 f W'et 25 3 min. 1min. 77 79 35 3 min. 1 min. 58 43 71 45 3 min. 1 min. 48 38 76 70 3 min.1 min. 24 34 73 100 3 min. 1 min. 32 71 80 25 15 hrs. 5 min. 25 50 15hrs. 5 min. 53

" Relative humidity.

** \Vet with water.

At the end of the above tests (held three minutes), the silk fabric wasdrastically and permanently distorted while the polyamide fabricreturned to essentially its former shape. Threads removed from thepolyamide fabric also retained their wavy form much better than did thesilk threads.

The polyamide fibers and fabrics are almost insensitive to moisture.'This is shown by the following experiment in which a sample of fiberhaving a denier of 1.1 obtained from polypentamethylene sebacamide wasdried by heating at 110 C. for 16 hours and immediately weighed. It wasthen stored at 25 C. at 50% relative hurnidity for five hours and againweighed. The

weights were 1.1184 g. and 1.1272 g. respectively, indicating that thefibers had absorbed 0.97% moisture. Viscose rayon fibers stored underconditions comparable absorbed about 8% moisture. The polyamide also hada higher ratio of wet to dry strength than the rayon. In general the wetstrength of the polyamide fibers is at least of their dry strength. Thebreaking point elongation of the fibers is usually above 20%. Theelastic properties of the fibers of this invention are noteworthy andare usually such that when the fiber is stretched 4% for one minute itrecovers at least 80% of its extension during the first minute ofrelease.

Example II A salt was prepared from hexamethylenediamine and adipic acidas follows: 144 parts of the amine was mixed with 174 parts of the acidin the presence of 1300 parts of 95% ethyl alcohol and 210 parts ofwater and the mass warmed until complete solution occurred. The mixturewas then cooled and the pure white crystals which separated out werefiltered off and recrystallized from 1300 parts of 95% alcohol and 200parts of water. The recrystallized material consisted of 247 parts. Itmelted at 183-184 C. and had the composition required for hexarnethylenediammonium adipate. It was converted into a fiber-forming polyamide byheating for three hours with an equal weight of mixed xylenol under theconditions described in Example I. The conductivity of the mixture fellfrom 0.0022 to 0.0000215 mhos and the absolute viscosity increased from0.14 to 20.4 poises. The precipitated polymer had an intrinsic viscosityof 1.2 and a melting point of about 263 C. as determined in a glass tubein the absence of oxygen. It was spun into oriented fibers as follows:The molten polymer was extruded from a spinneret at 284-292 C. under agas pressure of 50 lbs. per sq. in. applied with oxygen-free nitrogen ata spinning rate of 300 ft. per minute and a drawing rate of 1020 ft. perminute (equivalent to 240% cold drawing). The spinneret employed had tenorifices each 0.0078 inch in diameter placed at the bottom of 0.125 inchcone-shaped protrusions extending downward from the face of thespinneret. The resultant fibers had a denier at break of 1.08 and atenacity at break of 4.32 g. per denier. The wet strength of thesefibers was slightly more than of the dry strength. A ll3-denier,70-filament, 4-twist per inch yarn made from fibers of this polymercould readily be knit or woven into fabrics of excellent properties.

Example III A mixture of two mols of hexamethylene diammonium adipateand 0.02 mol. of adipic acid (viscosity stabilizer) was placed in atwo-liter, silver-lined autoclave equipped with an 18:8 stainless steel(i. e., 74% iron, 18% chromium, 8% nickel, and less than 0.2% carbon)stirrer and an 18:8 stainless steel steam-heated reflux condenser, thetop of which was connected through a water-cooled downward condenser toa receiver. Air was removed from the autoclave by evacuation, followedby filling with nitrogen and evacuating again. sure of 80 lbs. was thenapplied. The nitrogen used for this purpose was commercial nitrogenwhich had been washed with sodium hydrosulfite sliver salt solution toremove substantially the last traces of oxygen. The stirrer was startedand the autoclave heated to 288 C. during 1.5 hours. The pressure wasthen reduced to atmospheric during 0.5 hour and the heating and stirringcontinued for 2.5 hours. The pressure was then reduced to 200 mm.absolute pressure for a few minutes. After cooling the polymer wasremoved from the autoclave as a white solid cake. It had an intrinsicviscosity of about 0.9, was essentially viscosity stable, and yieldedgood fibers on spinning from melt using a constant volume delivery pumpofthe type used in viscose spinning (Zenith gear pump, type A-l).

Example IV Chemically equivalent amounts of sebacic acid andpentamethylenediamine were heated for two hours in a closed vessel at220240 C. This gave a low polymer. The vessel was then opened to permitthe removal of the water formed in the reaction. On heating the polymerfor one hour at 230240 C. under an absolute pressure of 1 mm. it wasconverted into high polymer. The product, polypentamethylene sebacamide,yielded fibers of good quality.

Example V A 40% solution of polyhexamethylene adipaniide (intrinsicviscosity, 1.38) in anhydrous phenol was placed in a brass tube whichheld a rayon spinneret having an orifice 0.006 inch in diameter. Thespinneret was situated a short distance above the surface of acoagulating bath seven feet in length containing a 3% aqueous solutionof sodium sulfide maintained at 70 C. The bath was provided with a motordriven guide roll placed close to the spinneret. Two other motor drivenrolls or bobbins were placed outside the bath: a take-up roll forwinding up the filaments as they left the bath and a drawing roll drivenat a higher rate of speed for cold A nitrogen pres- I drawing thefilaments. The polyamide solution was extruded from the spinneret at atemperature of 140 C. under a nitrogen pressure of 50 lbs. into thecoagulating bath. Drawing of the filaments in the bath was minimized bypassing the filaments over the guide roll which was synchronized withthe take-up roll. The wet filaments passed from the take-up roll to thedrawing roll. The peripheral speed of the take-up roll was 46 ft./min.and that of the drawing roll 167 ft./min. which is equivalent to 263%cold drawing. The cold drawn filaments or fibers were then washed withwater and dried. The fibers had a denier of 3.6, a residual elongationof 44%, a denier at break of 2.5, and a tenacity of 4.34 g. per denierat break.

Example VI A 25% solution of polyhexamethyleneadipamide (intrinsicviscosity, 1.35) in a solvent mixture consisting of approximately 89%phenol and 1 water was spun from a spinneret having 40 orifices of 0.004inch diameter into a coagulating bath consisting of a 4% aqueous sodiumhydroxide solution maintained at 75 C. The spinneret was immersed in thecoagulating bath. The spinning rate was 24 ft./min. and the drawing rate83 ft./min., equivalent to 246% cold drawing. The cold drawing wascarried out before washing the filaments. The resultant fibers afterwashing and drying had the following properties: denier, 0.9; denier atbreak, 0.518; tenacity based on the denier at break, 4.9 g. per denier;residual elongation, 74%.

Example VII A 29.2% solution of polyhexamethylene adipamide (intrinsicviscosity, 1.48) in formic acid was dry spun in an apparatus consistingof a brass tube holding a spinneret which was attached to anelectrically heated drying cell 6 ft. in length and having across-section 7 inches square. The cell had an orifice at the bottomthrough which the filaments could be removed and wound up on amotor-driven drum. A second drum also outside the cell driven at ahigher rate was provided for cold drawing the filaments. The top of thecell was provided with small air inlets, and a downward current of airwas maintained in the cell by means of a suitable suction tube attachednear the bottom. The polyamide solution in the spinneret was maintainedat room temperature, i. e., approximately 25 C. The solution wasextruded through the spinneret orifice (diameter, 0.004 inch) under 150lbs. nitrogen pressure. The temperature of the cell was maintained atapproximately 70 C. The spinning rate (peripheral speed of first drum)was 80 ft./min. and the drawing rate (peripheral speed of second drum)196 ft./min., corresponding to 145% cold drawing. After cold drawing thefibers were kept at 100 C. for minutes. The resultant fibers had adenier of 2.25, a denier at break of 0.80, a tenacity of 4.73 g. perdenier at break, and a residual elongation of 180%. The wet strength ofthese fibers was 4.2 g. per denier and the strength of knotted fiberswas 3.7 g. per denier. The high residual elongation of these fibers ischaracteristic of fibers spun from formic acid solution by the drymethod even when the fibers have been cold drawn more than 100% duringspinning.

While filaments of small diameter (0.00015- 0.0015 inch, correspondingroughly to 0.110.0 denier) are the most useful for the preparation ofyarns and fabrics, filaments of other sizes can be prepared from thepolyamides of this invention. For example, it is possible to preparelarger filaments which are useful as bristles, artificial straw, tennisstrings, fishline leaders, musical instrument strings, dental fioss,horse hair substitutes, mohair substitutes, and the like from thefiber-forming polyamides by the methods herein described. It is alsopossible to prepare large filaments by fusing together or uniting bymeans of an adhesive a plurality of small filaments. Large filaments canalso be prepared by cutting films or sheets into small strips. Whilethese strips are not round, they are useful for many purposes.

Filaments having diameters ranging from 0.003 to 0.060 inch areespecially suitable as bristles. Products of this type can be used ineither the undrawn or drawn (oriented) form. They have good snap,toughness, and resistance to water,

which make them useful in the manufacture of brushes, combs, and thelike. For the preparation of these large filaments, spinning of thepolyamide from melt through spinnerets having large orifices is mostsatisfactory, although solution spinning can also be employed as amethod of preparation. The large diameter filaments are less susceptibleto cold drawing than the smaller filaments. However, the drawing isgreatly facilitated by soaking the filaments in water, and/or warmingthem, e. g., to 100 C., prior to the drawing operation, as described incopending application Serial Number 125,887, filed February 15, 1937.The following is an example of the manufacture of large filaments orbristles:

Example VIII Following the general method described in the precedingexample, a 40% solution of polyhexamethylene adipamide (intrinsicviscosity, 1.38) in phenol was dry spun from a spinneret having a 0.02inch orifice under a pressure of lbs. The head temperature employed was130 C. and

the cell temperature 203 C. The large filaments or bristles thus formedwere not cold drawn. The small amount of phenol retained in the bristleswas removed by washing them with water and then drying them at 100 C.for one hour. The bristles had good snap, flexibility, and toughness.

It will be seen from the foregoing description that the recurringstructural units of my polyamides may be represented by the generalformula .N(a)-G'-N(a)-G"-. in which a and a are hydrogen or monovalenthydrocarbon radicals, G is a divalent hydrocarbon radical and G" is adivalent acyl radical. The most easily prepared fiber-forming polyamidesin this field are those having structural units of the general type.NH-GNH--G". I in which G and G" are defined as above, the sum of theradical lengths of G and NH--G-NH being at least 9. A particularlyvaluable group of polyamides from the standpoint of fiberformingqualities are those having structural recurring units which mayberepresented by the general formula .NHCI-IzRCHzNHCOCI-IzRCHzCO.

in which R and R are divalent hydrocarbon radicals of the types alreadydescribed. It will be noted that all of the polyamides'in the foregoingexamples are of this type. It will be noted further that thesepolyamides have recurring structural units of the general typeNHCH2(CH2) xCH2NI-ICOCH2(CH2) yCHaCO in which at and y are integers andin which :1: is at least two. High viscosity polyamides (intrinsicviscosity preferably above 0.6) of this select class are readily spunand give fibers of excellent quality.

It can be readily seen from the above examples that the importantfeature of the process of this invention is that the diamine and dibasicacid or amide-forming derivative, or the low molecular Weightnon-fiber-forming polyamide therefrom, must eventually be reacted orfurther reacted under conditions which permit the formation of a veryhighly condensed polyamide. In other words, the heating must becontinued at such a temperature and for such a period of time that theproduct can be drawn into oriented fibers, and this point is reachedessentially only when the intrinsic viscosity has risen to at least 0.4.In the preparation of some of my new fiber-forming polyamides, it may beadvantageous to apply the principles of molecular distillation describedin U. S. 2,071,250.

It will be evident that the present invention describes a wholly new andvery valuable type of synthetic fiber, and is therefore an outstandingcontribution tothis art because the new fibers are made bya whollysynthetic process and because they have unusual properties, beingstrong, flexible, elastic, insensitive to moisture, etc. to a remarkabledegree. They can be used to advantage either as continuous fibers or asstaple fibers, e. g., lengths of,1 to 6 inches. The fact that they showby X-ray diffraction patterns orientation along the fiber axis (acharacteristic of natural fibers and fibers derived from high molecularWeight natural substances) places them in the field of true fibers.

It is to be understood that my invention comprises also fibers, etc.,prepared from interpolyamides, e. g., a polyamide derived from thereactionof two or more diamines with one or more dibasic acids. Myfibers can also be prepared from mixtures of preformed polyamides.

' It is to be understood further that yarns and fabrics prepared fromthe synthetic polyamide fibers are within the scope of my invention. Theyarns can be prepared from either the continuous or staple fibers. Aconvenient method for making a polyamide yarn comprising staple fibersconsists indrawing a continuous thread or sliver consisting of amultiplicity of. substantially parallel continuous filaments, eitheroriented or unoriented, until the filaments are reduced to staple andtwisting (drafting) the sliver. If unoriented filaments are used in thisprocess the filaments draw down to a much greater extent before breakingthan in the case of previously described filaments, e. g., viscose oracetate rayon. My fibers and yarns can be knit, woven, or otherwiseformed into fabrics of widely different types. The excellent elasticrecovery of my fibers makes them especially useful in the preparation ofknitted wear, such as stockings, gloves, sweaters, underwear, suits,etc. My fibers are also useful in making sewing thread.

It is within the scope of my invention to use synthetic polyamide fibersand yarns in admixture with other types of fibers or yarns in thepreparation of mixed fabrics. As examples of other types of fibers andyarns which may be used in conjunction with my artificial fibers mightbe mentioned regenerated cellulose, spun or staple regeneratedcellulose, acetate rayon, staple acetate rayon, silk, silk waste, Wool,linen, and cotton. In these combinations the polyamide fibers may beused as continuous filaments or in the form of staple fibers. The mixedfabrics may be prepared by using different types of yarn, e. g., apolyamide yarn and a spun viscose rayon yarn, or by using yarns made upof mixtures of different types of fibers. When the latter method isemployed, the mixed yarns can be prepared by incorporating the polyamidefibers with the other fibers at any stage in the preparation of theyarn. For this purpose twisting or doubling methods may also beemployed. The mixed yarns may then be used in the preparation of wovenor knitted fabrics or may be used in conjunction with other yarns, e.g., in the preparation of woven fabrics. Polyamide yarn may be used ineither the warp or the filling. Novel effects are obtained by usingpolyamide yarns and other types of yarn intermittently in either thewarp, filling, or both. Likewise in the preparation of knitted fabricsthe different yarns may be fed into the knitting machine. The polyamidefibers impart increased strength to the fabrics.

My invention includes also the dyeing of the fibers, yarns, and fabricsmentioned above. The synthetic polyamides have a strong afiinity fordyes and can be dyed rapidly, permanently and directly with the dyesordinarily used for W001 and silk. For example, they can be dyed verysatisfactorily with dyes of the acid group, e. g., dyes of Color IndexNumbers 714 and 640; dyes of the chrome or acid mordant group, e. g.,dyes of Color Index Numbers 203 and 720; and dyes of the direct orsubstantivegroup, e. g., dyes of Color Index Numbers 365 and 512.Furthermore, they can be dyed with vat dyes, particularly those of theIndigoid and Thioindigoid classes, e. g., dyes of Color Index Numbers1177 and 1211. In this respect my products are superior to silk andwool, for the alkaline medium in which vat dyes can be used is moredamaging to silk and wool. My products can also be dyed satisfactorilywith dyes of the sulfur class. Union or mixed fabrics containing myfibers and other types of fibers, e. g.,

animal or cellulosic fibers, can also be dyed satisfactorily,particularly with dyes of the acid and direct groups. Thus, unionfabrics composed of my fibers and wool or of my fibers and regeneratedcellulose are satisfactorily dyed with dyes of these groups.

The following typical example, which is not to be considered aslimitative, is given to illustrate the dyeing of a synthetic polyamideyarn. The yarn was entered into a dyeing bath prepared with 1% of bluedye of Color Index Number 1088, 10% Glaubers salt, and 3% of sulfuricacid, the percentages being based on the weight of the yarn. The bathwas boiled for 0.5 hour, 1% sulfuric acid was added, and the boilingcontinued for an additional 025 hour. The yarn was then removed, rinsed,and dried, resulting in a satisfactory dyeing of good fastness to light.Fabrics can be dyed similarly.

While my polyamide fibers are normally lustrous, their luster can bereduced or destroyed by various means. The most satisfactory method forpreparing low luster polyamide fibers, however, consists in preparingthese fibers from a polyamide or polyamide solution containing dispersedtherein a finely divided substance which is inert toward the polyamide,is incompatible therewith at ordinary temperatures, and has an index ofrefraction differing from that of the polyamide. Pigment-like materialsare generally good delusterants. As examples of such delusterants mightbe mentioned titanium dioxide, zinc oxide, zinc sulfide, barium sulfate,carbon black, and copper phthalocyanine pigment. However, many organiccompounds, e. g., non-phenolic polynuclear compounds, also function asdelusterants.

It will be apparent that the polyamides herein described are most usefulin the form of filaments and fibers. Many other valuable artificiallyshaped objects may, however, be prepared from them by suitablemodification of the general methods herein described. For example,films, foils, sheets, ribbons, bands, rods, hollow tubing, and the likecan also be prepared from them. In general, however, these products arenot clear but are translucent or opaque, unless they are prepared by thespecial processes described in copending applications Serial Number125,927, filed February 15, 1937, by W. E. Catlin, and Serial Number125,926, filed February 15, 1937, by G. D. Graves. In these variousapplications the polyamides may be used alone or in admixture with otheringredients, such as cellulose derivatives, resins, plasticizers,pigments, dyes, etc.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that I do not limit myself to the specific embodimentsthereof except as defined in the appended claims.

I claim:

1. In the manufacture of polymeric materials the steps which compriseheating at polyamideforming temperatures a diprimary diamine withapproximately equimolecular proportions of a member of the groupconsisting of dicarboxylic acids in which each carboxyl group isattached to an aliphatic carbon atom, amide-forming derivatives of suchdicarboxylic acids, and amideforming derivatives of carbonic acid, andcontinuing such heating until a polymer is produced which is capable ofyielding continuous filaments that can be tied into hard knots.

2. A process which comprises contacting a diprimary diamine in whicheach amino group is attached to an aliphatic carbon atom withapproximately equimolecular proportions of a dicarboxylic acid in whicheach carboxyl group is attached to an aliphatic carbon atom, therebyforming a salt and heating said salt at polymerizing temperatures withremoval of water of reaction until a polymer is produced which iscapable of yielding continuous filaments showing by characteristic X-raydiffraction patterns orientation along the fiber axis.

3. In the manufacture of polymeric materials the steps which compriseheating at polyamideforming temperatures a diprimary diamine withapproximately equimolecular proportions of a member of the groupconsisting of dicarboxylic acids in which each carboxyl group isattached to an aliphatic carbon atom, amide-forming derivatives of suchdicarboxylic acids, and amideforming derivatives of carbonic acid, andcontinuing such heating with removal of the byproduct of reaction untila polymer is produced which is capable of yielding continuous filamentsshowing by characteristic X-ray diffraction patterns orientation alongthe fiber axis.

4. A process which comprises heating at polyamide-forming temperaturesunder substantially oxygen-free conditions a diprimary diamine, in whicheach amino group is attached to an aliphatic carbon atom, withapproximately equimolecular proportions of a member of the groupconsisting of dicarboxylic acids in which each carboxyl group isattached to an aliphatic carbon atom, amide-forming derivatives of suchdicarboxylic acids, and amide-forming derivatives of carbonic acid, thereactants being selected such that the sum of their radical lengths isat least 9, and continuing the heat treatment until a polymer isproduced which is capable of yielding continuous filaments that can beformed into fabric.

5. A process which comprises reacting at polyamide-forming temperaturesand between 180-300 C. a diprimary diamine of the formula NHzCHzRCHzNHzwith approximately equimolecular proportions of a dicarboxylic acid ofthe formula HOOCCI-IzRCI-IzCOOH, in which R and R are divalenthydrocarbon radicals free from olefinic and acetylenic unsaturation andin which R has a chain length of at least two carbon atoms, andcontinuing the heat treatment with removal of the Icy-product ofreaction until a polymer is produced which is capable of yieldingcontinuous filaments that can be formed into a fabric.

6. The process set forth in claim 5 in which R is (CH2)X and R is (CH2)x and being integers, and a: being at least 2.

'7. A process which comprises heating at polyamide-forming temperaturesin the presence of an inert organic diluent a diprimary diamine, inwhich each amino group is attached to an aliphatic carbon atom, withapproximately equimolecularproportions of a member of the groupconsisting of dicarboxylic acids in which each carboxyl group isattached to an aliphatic carbon atom, amide-forming derivatives of suchdicarboxylic acids, and amide-forming derivatives of carbonic acid, thereactants being selected such that the sum of their radical lengths isat least 9, and continuing the heat treatment until a polymer isproduced which is capable of yielding continuous filaments that can beformed intofabrics.

8. The process set forth in claim 7 in which the organic diluent is asolvent for the reactants and reaction product.

9. The process set forth in claim 7 in which the -hydrocarbon radicalsfree from olefinic and acetylenic unsaturation and R having a chainlength of at least two carbon atoms.

11. The process set forth in claim 7 in which the organic diluentconsists essentially of a monohydric phenol as a solvent for thereactants and reaction product.

12. A process which comprises reacting at polyamide-forming temperaturesa diprimary diamine of the formula NHzCHzRCI-IzNI-Iz with approximatelyequimolecular proportions of an amideforming derivative of adicarboxylic acid of the formula HOOCCI-IzR'CHzCOOI-I, in which R and R.are divalent hydrocarbon radicals free from olefinic and acetylenicunsaturation and in which R has a chain length of at least two carbonatoms, and continuing the reaction until a polymer is produced capableof yielding continuous filaments which can be knitted into a fabric.

amine of formula NH2CH2RCH2NH2 and a dicarboxylic acid of formulaHOOCCI-IzR'CHzCOOI-I and heating the mass at polyamide-formingtemperatures in the substantial absence of oxygen and with removal ofwater of reaction until the polymer formed is capable of being spun intofilaments which can be cold drawn into fibers showing by characteristicX-ray diffraction patterns orientation along the fiber axis, R and Rbeing defined as in claim 5.

15. A process for making a viscosity stable polyamide Whose viscosity issubstantially unaltered by heating at its melting point, said processconsisting of heating at polyamide-forming temperatures a mixture ofreactants which is capable of yielding a fiber-forming polyamide andwhich contains one of said reactants in 0.1 to 5.0 molar per centexcess, said mixture of reactants comprising a diprimary diamine, inwhich each amino group is attached to an aliphatic carbon atom, and amember of the group consisting of dicarboxylic acids in which eachcarboxyl group is attached to an aliphatic carbon atom, amide-formingderivaties of such dicarboxylic acids, and amideforming derivatives ofcarbonic acid, and continuing said heating until a polyamide is producedwhich can be formed into continuous filaments capable of being made intofabric.

16. A process which comprises contacting a diprimary diamine of formulaNI-IzCI-IzRCI-IzNHz and a dicarboxylic acid of formula HOOCCHzR'CHzCOOH,

in which R and R are divalent hydrocarbon radicals free from olefinicand acetylenic unsaturation and in which R, has a chain length of atleast two carbon atoms, isolating the salt thereby formed, and heatingsaid salt at polyamideforming temperatures with removal of water ofreaction until a polymer is produced which has an intrinsic viscosity ofat least 0.4.

17. A process for making polymeric materials which comprises heating atpolyamide-forming temperatures in the absence of any appreciable amountof oxygen, a salt obtainable from a diprimary diamine in which eachamino group is attached to an aliphatic carbon atom and a dicarboxylicacid in which each carboxyl group is attached to an aliphatic carbonatom, and continuing said heating under conditions permitting theremoval of water of reaction until the polymer former is capable ofyielding oriented fibers.

18. A step in a process for making polymeric materials, which comprisessubjecting a poly amide derived from a diprimary diamine of formulaNHzCHzRCHzNI-Iz and a. dicarboxylic acid of formula HOOCCHzRCHzCOOH,said polyamide being incapable of yielding continuous filaments, tocontinued polymerizing heat treatment under conditions permitting theescape of volatile by-product until the polymer formed is capable ofbeing drawn into continuous filaments showing by characteristic X-raydiffraction patterns orientation along the fiber axis, R and R beingdefined as in claim 5.

19. In the manufacture of highly polymeric materials, the steps whichcomprise forming a low molecular Weight polyamide by heating atpolyamide-forming temperatures under superatmospheric pressureapproximately equimolecular proportions of a diprimary diamine offormula NHzCHzRCI-IzNI-Iz and a dicarboxylic acid of formulaHOOCCHZR'CHZCOOH, and then continuing the heating at polyamide-formingtemperatures under conditions permitting the escape of water of reactionuntil the resultant polymer is capable of being spun into pliablefilaments, R and R being defined as in claim 5.

20. A process for manufacturing polymers which comprises heating atpolyamide-forming temperatures approximately equimolecular proportionsof hexamethylenediarnine and adipic acid and continuing such heatingwith removal of the water of reaction until the polyamide formed iscapable of yielding continuous fibers showing by characteristic X-raydiffraction patterns orientation along the fiber axis.

21. A polyamide obtainable by condensation polymerization from a diamineand a dibasic carboxylic acid, said polyamide being capable of beingformed into fibers showing by characteristic X-ray patterns orientationalon the fiber axis.

22. A polyamide capable of being formed into continuous filamentsshowing by characteristic X-ray diffraction patterns orientation alongthe fiber axis, said polyamide being one which is obtainable bycondensation polymerization from a diprimary diamine and a dicarboxylicacid and which has an intrinsic viscosity of at least 0.4

23. A polyamide comprising the reaction product of a diprimary diamine,in which each amino roup is attached to an aliphatic carbon atom, withapproximately equimolecular proportions of a member of the groupconsisting of dicarboxylic acids in which each carboxyl group isattached to an aliphatic carbon atom, amide-forming derivatives of suchdicarboxylic acids, and amideforming derivatives of carbonic acid, saidpolyamide being capable of being formed into pliable fibers which can bemade into textile fabrics.

24. A polyamide obtainable by condensation polymerization from a diamineand a dibasic carboxylic acid, said diamine being of the formulaNH2CH2RCH2NH2 and said dibasic acid being of the formula HOOCCH2RCH2COOHin Which R and R are divalent hydrocarbon radicals free from olefim'cand acetylenic unsaturation and in which R has a chain length of atleast two carbon atoms, said polyamide being capable of yieldingcontinuous filaments which can be tied into hard knots.

25. The polyamide set forth in claim 24 in which R is (CI-12M and R is(Cl-12%,, a: and y being integers, and a: being at least 2.

26. A linear polyamide having recurring structural units of the generalformula where G is a divalent hydrocarbon radical in which the atomsattached to the NII groups are aliphatic and G is a divalent aliphaticacyl radical, the sum of the radical lengths of G and NHG-NH- being atleast 9, said polyamide being capable of yielding continuous filamentswhich can be formed into a fabric.

27. A polymer capable of being drawn into continuous filaments which canbe formed into fabrics, said polymer yielding, upon hydrolysis withhydrochloric acid, a mixture of substances comprising a diaminehydrochloride and a dibasic carboxylic acid.

28. A synthetic linear condensation polymer having an intrinsicviscosity of at least 0.5, said polymer yielding, upon hydrolysis withhydro chloric acid, a mixture of substances comprising a diaminehydrochloride and a dicarboxylic acid.

29. A viscosity stable polyamide whose viscosity is substantiallyunaltered by heating at its melting point, said polyamide beingobtainable by condensation polymerization from a mixture of diamine anddibasic carboxylic acid containing one of said reactants in 0.1 to 5.0molar per cent excess, and said polyamide being capable of yieldingcontinuous filaments which can be formed into fabric.

30. A polyamide obtainable by heating at polyamide-forming temperaturesat least two different diamines with at least one dibasic carboxylicacid, said polyamide having an intrinsic viscosity of at least 0.4.

31. A polyamide obtainable by heating at polyamide-forrm'ng temperaturesat least one diamine with at least two different dibasic carboxylicacids, said polyamide having an intrinsic viscosity of at least 0.4.

32. A synthetic linear condensation polyamide capable of being formedinto fibers showing by characteristic X-ray patterns orientation alongthe fiber axis, said polyamide being polymeric hexamethylene adipamide.

33. A process for making synthetic fibers from polyamides derived fromdiamines and dibasic carboxylic acids which comprises spinning afilament from said polyamide and subjecting said filament tocold-drawing under tension until it shows by characteristic X-raydiffraction patterns orientation along the fiber aids.

34. The process set forth in claim 33 in which the polyamide is in themolten state.

35. The process set forth in claim 33 in Which the polyamide is insolution and solvent is removed from the filament before it iscold-drawn.

36. A process for making artificial fibers which comprises forming intoa filament a polyamide having an intrinsic viscosity of at least 0.4,and subjecting said filament to stress to produce a fiber showing bycharacteristic X-ray diffraction patterns orientation along the fiberaxis, said polyamide being obtainable by condensation polymerizationfrom a diamine of formula NH2CI-I2RCH2NH2 and a dicarbcxylic acid offormula HOOCCHzR'CI-IaCOOI-I in which R and R are divalent hydrocarbonradicals free from olefinic and acetylenic unsaturation and in which Rhas a chain length of at least two carbon atoms.

37. A process which comprises extruding into filaments a solution of asynthetic polyamide which is obtainable by condensation polymerizationfrom a diamine and a dibasic carboxylic acid, evaporating the solventfrom the filaments, and subjecting the filaments to stress until theyare formed into fibers useful in the manufacture of fabric.

38. A process which comprises extruding filaments from a solution of asynthetic polyamide into a liquid which dissolves the solvent of thesolution but not the polyamide, and subjecting the filaments to stressuntil they are formed into fibers useful in the manufacture of fabric,said polyamide being that obtainable by condensation polymerization froma diamine and a dibasic carboxylic acid.

39. A process for making fibers which comprises extruding filaments froma solution of a synthetic polyamide into a liquid which dissolves thesolvent of said solution but not the polyamide, and subjecting thefilaments to stress until they are formed into fibers capable of beingtied into hard knots and useful in the manufacture of fabric, saidpolyamide having an intrinsic viscosity above 1.0 and being obtainableby condensation polymerization from a diamine and a dibasic carboxylicacid.

40. A polyamide obtainable by condensation polymerization from a diamineand a dibasic carboxylic acid, said polyamide being in the form of afilament showing by characteristic X-ray diffraction patternsorientation along the fiber axis.

41. A polyamide in the form of a filament which yields, upon hydrolysiswith hydrochloric acid, a diamine hydrochloride and a dibasic carboxylicacid.

42. A polyamide in the form of a filament which yields, upon hydrolysiswith hydrochloric acid, an aliphatic diprimary diamine hydrochloride andan aliphatic dibasic carboxylic acid, the sum of whose radical lengthsis at least 9, said filament being capable of being tied into hardknots.

43. A delustered filament comprising a delustering agent and a polyamideobtainable by condensation polymerization from a diamine and dibasiccarboxylic acid.

44. A polymer in the form of a crenulated pliable fiber which yields,upon hydrolysis with hydrochloric acid, a mixture of substancescomprising a diamine hydrochloride and a dibasic carboxylic acid, saidfiber being capable of being formed into a yarn which can be woven, intoa fabric.

45. A synthetic polymer in the form of a pliable filament, said polymerbeing obtainable by condensation polymerization from a diprimary diamineof formula NH2CH2RCH2NH2 and a dicarboxylic acid of formulaHOOCCHzRCHzCOOI-I, wherein R and R are defined as in claim 5.

46. A synthetic polymer in the form of staple fibers which are capableof being formed into useful yarns, said polymer being obtainable bycondensation polymerization from a diamine and a dibasic carb-oxylicacid.

47. An artificial filament comprising polymeric hexamethylene adipamide.

48. A dyed fabric, said fabric containing filaments which yield, onhydrolysis with hydrochloric acid, a diamine hydrochloride and a dibasiccarboxylic acid.

49. A fabric comprising filaments derived from a synthetic linearcondensation polymer, said filaments yielding, upon hydrolysis withhydrochloric acid, a diamine hydrochloride and a dibasic carboxylicacid.

50. A mixed fabric comprising synthetic poly= amide filaments, saidpolyamide being obtainable by condensation polymerization from a diamineand a dibasic carboxylic acid.

51. A synthetic polymer in the form of a film,

said polymer being obtainable by condensation polymerization from adiamine and a dibasic carboxylic acid.

52. A synthetic polymer in the form of an artificial filament having adiameter ranging from 0.003 to 0.06 inch, said polymer yielding, uponhydrolysis with hydrochloric acid, a mixture of substances comprising adiamine hydrochloride and a dibasic carboxylic acid.

53, A brush containing bristles which are obtainable by condensationpolymerization from a diamine and a dibasic carboxylic acid.

54. A synthetic polyamide capable of being formed into fibers showing bycharacteristic X-ray patterns orientation along the fiber axis, saidpolyamide being polymeric pentamethylene adipamide.

55. A synthetic polyamide capable of being formed into fibers showing bycharacteristic X-ray patterns orientation along the fiber axis, saidpolyamide being polymeric tetramethylene sebacamide.

56. The delustered filament set forth in claim 43 wherein saiddelustering agent is titanium dioxide.

WALLACE HUME CAROTHERS.

